Adequate amino acid (AA) nutrition is essential for the health and well- being of humans and animals alike. Because AAs have no storage pool, the development of an essential AA deficiency can occur rapidly, particularly if a mild state of protein deficiency already exists. Since AA supplements have become fashionable, and may especially be used by dieters, AA imbalance should be recognized as a potential health hazard. Moreover, individuals with cancer cachexia, disorders of AA metabolism, and other metabolic aberrancies may also suffer AA disproportion. AA deficiencies have been shown to compromise growth and any bodily function that depends on protein synthesis, such as wound healing. However, the growth reduction attributed to AA imbalance is actually secondary to the decreased food intake, an anorectic response to the AA deficiency. The long-term goal of the work in this laboratory is to understand how AA deficiency is recognized by the body, and how this deficiency is expressed in a readily available behavioral measure, food intake. Given the importance of AA nutrition, it is imperative that we gain a better understanding of the basic mechanisms by which AA imbalance affects feeding behavior. A well defined nutritional model using AA imbalanced (IMB) diets is available for these studies. The piriform cortex (PC) of the brain has been implicated as the prime candidate for the sensor of AA deficiency in the IMB-diet model. The primary event in the PC after ingestion of IMB is a drop in the concentration of the limiting AA. We have also determined that norepinephrine, cAMP, nitric oxide, serotonin and alterations in RNA and protein synthesis may be involved in the neural responses to IMB. However, although we have identified these different systems as being involved, we do not understand how they interact with the limiting AA in the initial molecular and cellular responses to IMB. Therefore, the major objective of this research is to determine the molecular mechanisms responsible for the recognition and rejection of diets that result in an AA deficiency. Specifically, we will determine how amino acids regulate gene expression in neurons of the PC. The following three Specific Aims will address these questions: SPECIFIC AIM 1: To obtain cDNA and genomic clones that correspond to genes regulated by amino acid deficiency in the PC, using both differential display and a subtracted cDNA library. SPECIFIC AIM 2: To further develop an in vitro system to dissect the complex regulation that occurs by amino acids in the PC using primary neuron cultures. SPECIFIC AIM 3: To determine if tRNA aminoacylation levels change in response to amino acid deficiency in PC neurons.